It is known in the manufacturing of power distribution apparatus to include automatic transformer tap changing that can adjust the power fed to factories, subdivisions, apartment houses, and other large loads as often as several times a day or more as the load varies. This load variation changes the voltage drop across substantially fixed resistances such as distribution wiring, requiring compensating adjustments in transformer tap connections.
The contact portion of a tap changer is in some embodiments fully immersed in insulating oil for cooling and reduction of arcing. The immersed switching events can nonetheless exhibit some arcing, which tends to break down the oil, leaving contaminating particles. In addition, the tap changer is normally not hermetically sealed, so that there is some opportunity in many systems for water vapor to enter the system, which vapor can be absorbed by the oil, can be entrained as a corrosion promoter, or can otherwise become an active contaminant.
It is further known in the power distribution industry to provide a surplus volume of oil in a reservoir in each unit of the apparatus in order to increase thermal mass and to promote thermal regulation without continuous recourse to pumping. Installation of filters and pumps permits periodic filtering to capture undesirable materials for subsequent removal. Industry has developed a variety of solutions to the power distribution and switching apparatus oil contamination problem. This has lead to diversity in the capabilities of the apparatus that controls such parameters as filtering system run time and run interval, as well as of styles, of filters. In some examples, the filter or the pump may be located inside the apparatus, so that it is necessary to deenergize, drain, and disassemble the apparatus simply to gain access to the pump and/or filter to troubleshoot it; in other examples, filtering resources are limited in capability with respect to the volume of oil in a device requiring filtering.
Accordingly, there is a need in the art for an apparatus and method for adapting pumped filter systems to accept more than one type of filter, as well as further adapting pumped filter systems to operate either in a heavily automated mode or with very detailed user command control.